1. Field of the Invention
The present invention relates to a digital audio signal coding system for coding music and sound signals through data compression and to a method therefor.
2. Description of the Prior Art
In a conventional audio signal coding system utilizing a band splitting method, the amount of quantization bit number has been so controlled that, a product of a down-sampling frequency and a quantization bit number, i.e., the amount of transmission data of each band conforms to the degree of contribution in the band in terms of articulation index (for example, refer to pages 56 through 61 of "High efficiency sound signal coding" written by Kazuo Nakata, published in 1986).
FIG. 5 shows a block diagram of a general audio signal encoding and decoding device. Referring to FIG. 5, designated by a reference numeral 18 is an encoder unit and numeral 19 is a decoder unit. The encoder unit 18 includes a band splitting section 20 for splitting an audio signal into a number of sub-bands, a quantizing and encoding section 21 for quantizing and encoding samples of each sub-band signal every specified amount of samples, a multiplexing section 22 for transmitting or recording each encoded sub-band signal, and a quantization bit number allocating section 23 for allocating a quantization bit number to every certain amount of samples of each sub-band signal when quantizing the samples. In the encoding stage, the bands have been split in such a way that each of the bands has the same degree of contribution in terms of articulation index, and the bit number has been allocated in such a manner that the product of a down sampling frequency and a quantization bit number allocated to every amount of samples, i.e., the amount of transmission data of each band conforms to the degree of articulation index contribution of the band.
On the other hand, the decoder unit 19 includes a demultiplexing section 24 for demultiplexing sub-band signals each transmitted or recorded in a multiplex form, a dequantizing and decoding section 25 for dequantizing and decoding the samples of the sub-band signals, and a band synthesizing section 26 for synthesizing the sub-band signals into a full-band audio signal.
According to such a conventional quantization bit control method in an audio signal coding device employing the conventional band splitting process described as above, the quantization bit number is controlled so that the amount of transmission data in each band conforms to the degree of contribution of the band in terms of articulation index. The above-mentioned method has been effective in efficiently coding data. However, in such a conventional way of quantization bit control, since whole data of auditory data such as music and sound recognized through human auditory sense is uniformly coded, such a conventional quantization bit control method is not satisfactory one for allocating more bits to data important for human sense, which means that the limited coding capacity is not used efficiently.